North American Network Operators Group

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Re: Jumbo Frames (was Re: MAE-EAST Moving? from Tysons corner toreston VA. )

  • From: Bill Woodcock
  • Date: Mon Jun 19 12:34:50 2000

    > Which is one of the reasons that we specified 1600 as the frame size 
    > for most line disciplines, such as PPP over Frame Relay, etc., since 
    > circa 1992....
    > PPP itself is 1500, matching ethernet, in the vain hope that folks 
    > would remember to distinguish "packet" data size from "frame" size. 

This problem is also one that plagues DSL, as many DSLAMs expect to see a
full Ethernet packet, including Ethernet header, inside the frame/atm
packet that comes in from the network.  They strip the frame/atm header,
and dump the contents onto the DSL/Ethernet wire.

If you're using frame relay on the backhaul, a max-length Ethernet packet
with both Ethernet and frame relay headers will obviously exceed the
1500-byte limit, and get truncated.  If you pull the Ethernet header out,
you need to get the DSLAM to generate a new one on the other side, which
many of them verge on not being smart enough to do.